Road grade can be simply defined as the instantaneous change in real or true vertical displacement (i.e. change in true elevation) per instantaneous change in horizontal displacement, over a given time interval, expressed as a percent. While this parameter is conceptually simple to calculate and understand, it is very difficult to measure accurately, in real-time, at high frequency by previously known methods using known apparatuses. For example, while a Global Positioning System (GPS) receiver can be used to acquire both of the needed variables—the change in true elevation as well as the change in horizontal displacement in traveling from one geographic location to another, instantaneous measurements of small elevation changes are very inaccurate using the GPS receivers that are available for civilian use. High resolution measurements needed for real-time measurement of undulating roadways and changing road grades typically found in the real world require the ability to accurately sense very small changes in true elevation. For example, climbing or descending an 8% road grade, which is a relatively steep road, results in a vertical velocity of only 0.5 m/s for a horizontal speed of 25 kilometers per hour. And railway grades are usually much smaller than this.
Although accurate elevation measurement is not needed for accurate road grade measurement (i.e. accurate elevation change and horizontal displacement change over the same time interval are what is needed), the present disclosure also teaches how to accurately determine true elevation in real-time.
Laboratory-based tailpipe emissions testing has been historically performed under a limited range of ambient conditions, vehicle speed cycles, and driving conditions. Because the number of vehicles has increased dramatically in recent years worldwide, and because vehicles have become increasingly computer-controlled, it has become necessary for government regulators and automobile manufacturers to better understand the emissions of vehicles across a wider range of operating conditions so that National Ambient Air Quality (NAAQ) standards can continue to be met in current ambient air pollution “attainment areas” and can eventually be met in current “non-attainment areas.” It has also become advantageous for vehicle manufacturers to be able to assess the effects of contemplated changes to vehicle emission control system designs and powertrain calibrations across a wider range of ambient and operating conditions, including road grades.
BEVs may become a significant factor of overall pollution from “stationary sources” in the future if they are produced in increasingly larger numbers because they will get their energy for battery charging from the power grid, which may remain heavily dependent on fossil fuels for power generation in the near term. And BEVs typically have a shorter range on a fill charge than a fully-fueled ICE vehicle. Therefore, it is important to understand the energy efficiency of BEVs in real-world driving, including variable road grades, to optimize their control systems, maximize their range, and minimize associated stationary source pollution.